[PATCH] tests/functional/test_vnc: Reduce raciness in find_free_ports()

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

Pass the port range as argument. In order to reduce races
when looking for free ports, use a per-target per-process
base port (based on the target built-in hash).

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
---
Based-on: <20240830133841.142644-33-thuth@redhat.com>
---
 tests/functional/test_vnc.py | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/tests/functional/test_vnc.py b/tests/functional/test_vnc.py
index b769d3b268..508db0709d 100755
--- a/tests/functional/test_vnc.py
+++ b/tests/functional/test_vnc.py
@@ -10,6 +10,7 @@
 # This work is licensed under the terms of the GNU GPL, version 2 or
 # later.  See the COPYING file in the top-level directory.
 
+import os
 import socket
 from typing import List
 
@@ -18,7 +19,6 @@
 
 VNC_ADDR = '127.0.0.1'
 VNC_PORT_START = 32768
-VNC_PORT_END = VNC_PORT_START + 1024
 
 
 def check_bind(port: int) -> bool:
@@ -41,9 +41,10 @@ def check_connect(port: int) -> bool:
     return True
 
 
-def find_free_ports(count: int) -> List[int]:
+# warning, racy function
+def find_free_ports(portrange, count: int) -> List[int]:
     result = []
-    for port in range(VNC_PORT_START, VNC_PORT_END):
+    for port in portrange:
         if check_bind(port):
             result.append(port)
             if len(result) >= count:
@@ -91,7 +92,10 @@ def test_change_password(self):
                     password='new_password')
 
     def test_change_listen(self):
-        a, b, c = find_free_ports(3)
+        per_arch_port_base = abs((os.getpid() + hash(self.arch)) % (10 ** 4))
+        port_start = VNC_PORT_START + per_arch_port_base
+        port_stop = port_start + 100
+        a, b, c = find_free_ports(range(port_start, port_stop), 3)
         self.assertFalse(check_connect(a))
         self.assertFalse(check_connect(b))
         self.assertFalse(check_connect(c))
-- 
2.45.2